Exemplary embodiments relate to a communication method for downlink transmission with a low peak to average power ratio (PAPR) and compatibility with long-term evolution (LTE)-based downlink transmission in an LTE-based mobile communication system in which the performance degradation may occur due to a high PAPR in multi-carrier transmission caused by non-linearity of a power amplifier in a base station including a satellite.
LTE-based downlink transmission is based on orthogonal frequency division multiplexing (OFDM). OFDM is an attractive downlink transmission scheme in many aspects. In particular, OFDM is robust to frequency selective channel conditions because of a relatively long OFDM symbol and a cyclic prefix (CP). Principally, a loss of signal caused by a frequency selective channel may be resolved by an equalizer at a receiving end. However, in a case of a terminal operating at a bandwidth greater than 5 megahertz (MHz), the equalizer may experience an excessively increasing degree of complexity. Since OFDM is inherently robust to frequency selective channel conditions, OFDM is particularly suitable for downlink transmission in a bandwidth greater than 5 MHz. In an LTE uplink, discrete Fourier-transform spread (DFTS)-OFDM single carrier transmission is used. The reason for single carrier modulation being used in an uplink is due to a lower PAPR of a transmitted signal than multi-carrier transmission, such as, OFDM. As a PAPR of a transmitted signal becomes lower, an average transmission power in a given power amplifier increases. Accordingly, single carrier transmission ensures a higher efficiency of a power amplifier, and this leads to increased coverage and reduced power consumption of a terminal.
In an LTE-based terrestrial mobile communication system, OFDM is used in a downlink relatively insensitive to a PAPR by the support of a power amplifier having a relatively high performance since OFDM is sensitive to a PAPR but flexible in frequency domain resource allocation, and DFTS-OFDM is used in an uplink sensitive to a PAPR by the use of a power amplifier having a relative low performance in a context of a terminal overhead even though DFPS-OFDM has many limitations in resource allocation for maintaining the single carrier properties. When compared to a terrestrial mobile communication system, a satellite mobile communication system is less concerned about frequency domain resource allocation because of frequency non-selective satellite channel properties, and experiences performance degradation caused by non-linearity of a satellite power amplifier in multi-carrier transmission in downlink since the power amplifier is very sensitive to a PAPR. In this instance, single carrier transmission is more effective for a satellite mobile communication system sensitive to a PAPR to improve the performance than multi-carrier transmission due to non-linearity of a power amplifier in a base station.
As a future mobile communication network is expected to evolve into a combination or cooperation of a terrestrial network and a satellite network, commonality between a satellite radio interface and a terrestrial radio interface is a primary consideration when implementing an integrated satellite/terrestrial mobile communication system, with a terminal overhead being taken into account. Particularly, in a circumstance in which an LTE-based terrestrial mobile communication system is given consideration as a next-generation international mobile telecommunications (IMT)-Advanced system, when a radio interface of a satellite mobile communication system maintains commonality with that of an LTE-based terrestrial mobile communication system, the satellite mobile communication system may reuse an existing terrestrial terminal, resulting in notable economic efficiency. In contrast, when commonality with a terrestrial network is excluded from consideration, a satellite mobile communication system may have reduced overhead of a satellite payload and may be fit for use in a satellite mobile communication environment by using a radio interface suited to a satellite environment. To use satellite and terrestrial services, a terminal needs a dual mode chip embedded in the terminal to support satellite and terrestrial radio interfaces. Accordingly, to ensure interoperability with an LTE-based terrestrial mobile communication system, an LTE-based satellite mobile communication system needs to support an integrated satellite/terrestrial terminal that achieves notable economic efficiency with no additional cost for reuse of an existing terrestrial LTE chipset even though the performance may experience modest degradation, and an integrated satellite/terrestrial terminal that provides a high-quality service suited to a satellite environment through upgrading functions of the terminal, while maintaining commonality with an LTE terrestrial network.